What Vacuum-Insulated Tubings and Casings Bring to Thermal Wells

This paper describes both design and economic considerations that lead to the selection of vacuum-insulated tubing (VIT) or vacuum-insulated casing (VIC) for the completion of thermal wells. The results shared in this paper are some of the parameters considered during thermal-well design: temperature on the casing and the tubing, and heat loss. Knowing these parameters, well integrity can be studied and the overall efficiency of the process estimated.

Introduction

The most common thermal enhanced-­recovery methods are cyclic steam stimulation, steamflooding, and steam-­assisted gravity drainage, which is widely used in Canada. The role of these thermal-recovery methods is to convey heat into the reservoir, mainly by convection. The temperature of the oil increases and its viscosity decreases significantly in the reservoir. These methods can substantially increase the oil production of a field, increase the recovery factor, or unlock some heavy-oil assets.

Typical steam-injection temperature is between 250 and 310°C; in a few cases, it could be greater than 310°C. This high-temperature application requires adapting the design of the injector wells to avoid any mechanical failure of the well or to mitigate heat loss through the well. VIT or VIC are solutions to some of these issues.

VIT technologies have evolved significantly since their first application. Different materials are used as insulation material, and several designs are proposed by the industry to achieve the best thermal-performance-vs.-cost equation.

A model was developed to assess the temperature of the different components of a well—tubing, casing, cementation, and ground—and to provide the heat loss occurring during the steam injection. The results show that the wide range of VIT thermal performance provides a range of casing temperatures. Thus, the casing thermal expansion or thermal loads resulting from this temperature increase range significantly.

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